An electronic synchronized sound recording and reproducing system to which the present invention appertains includes a sound recording and reproducing apparatus a typical example of which is a sound tape recorder which reproduces sound information from a tape as a series of audible sounds such as, for example, a music which is herein referred to as base music. The tape recorder is provided in combination with a sequencer module in which sound information to be reproduced as a series of audible sounds, or an additional music, is preliminarily programmed. The tape recorder and the sequencer module are operated in synchronism with each other so that the base music recorded on the tape set on the tape recorder and the additional music memorized in the sequencer module are reproduced concurrently.
In an electronic synchronized sound recording and reproducing system of the described general nature, it is desirable that both of the base and additional musics be reproduced at tempos reflecting the operator's emotional expressions. It has for this purpose been proposed and put into practice to have external tempo information fed to the sequencer module in which the additional music is preliminarily memorized. An example of an electronic synchronized sound recording and reproducing system having such a capability is taught in Japanese Patent Application No. 56-23651.
In a system shown in this Patent Application, a synchronizing signal generator is connected between a tape recorder and a sequencer module and has a basic function to provide synchronism between the two series of sound information, or base and additional musics, to be reproduced by the tape recorder and the sequencer module, respectively, during playback mode of operation of the system. The system has an additional capability of memorizing beat signals produced by an operator who beats time with a tapping key while listening to the music being reproduced from the sound track of the tape on the tape recorder during write-in mode of operation of the system. These beat signals are fed to the tape recorder and are recorded on another record track, a beat track, of the tape as the beat information which represents the tempos expressed by the operator. During the write-in mode of operation, signals are also produced while are indicative of the time intervals between successive beat signals representing the series of beats. Thus, the number of the clock signals which intervene between any successive two beat signals is indicative of the time interval between two successive beats. These clock signals are memorized into an internal memory provided in the synchronizing signal generator.
During the playback mode of operation which follows such a write-in mode of operation, the tape recorder reads the beat signals from the beat track of the tape while reproducing the sound information from the sound track of the tape. The beat signals are converted into synchronizing signals each of which is transferred to the synchronizing signal generator from the tape recorder. The synchronizing signal generator accesses any one of the addresses of the internal memory therein each time the signal generator receives a synchronizing signal and thus reads the time intervals stored at the selected address of the memory. A total of twenty four MIDI (Musical Instrument Digital Interface) clock pulses are generated for each of these time intervals. To produce such MIDI clock pulses, the internal memory of the synchronizing signal generator in which the time intervals between the successive beat signals are memorized, during write-in mode of operation, in the form of the number of bits each having a time duration of 417 microseconds and the number of frames each consisting of eighty bits, in compliance with the SMPTE (Society of Motion Picture and Television Engineers) Standards. The time duration T.sub.i of an MIDI clock pulse is calculated, during playback mode of operation, on the basis of these numbers of frames and bits, or frame count (X.sub.i) and bit count (Y.sub.i), in accordance with the following formula: EQU T.sub.i =(417*80*X.sub.i +417*Y.sub.i)/24 (1)
The MIDI clock pulses thus generated are supplied in succession from the synchronizing signal generator to the sequencer module, which generates sound signals on the basis of the tempo information represented by this series of MIDI clock pulses and the sound information memorized in the sequencer module per se. These sound signals are fed to a subsequent synthesizer module and is synthesized into an additional music which is to be produced from a sound generator in synchronism with the base music reproduced from the tape in the tape recorder.
A known synchronized sound recording and reproducing system of the described nature has had a drawback which results from the fact that there are available no specific indications of those physical locations of the recording tape at which the individual beat signals occur on and along the code track of the tape. For this reason, the beat signals recorded on the tape can be detected from the tape not in terms of the physical locations on the tape but in terms of the sequence in which the successive beat signals occur along the tape. The synchronization between the beat signals read from the tape and the time intervals between the successive beat signals read from the internal memory of the system is normally achieved on the basis of a certain established time-axis correlation between the two kinds of time bases. It may however happen that such a time-axis correlation be lost or deranged for one cause or another as, typically, when a dropout of a beat signal takes place on the tape. When this occurs, the time base to dictate the tempo of the additional sound information to be synthesized through the sequencer module fails to match the time base to dictate the tempo of the sound information to be reproduced from the tape recorder. The synchronizing signal generator of a prior-art synchronized sound recording and reproducing system of the described nature could not recover the proper correlation between the aforesaid two kinds of time bases once such correlation is lost or deranged. Failure to recover the correlation would thus lead to a mismatch between the sound information being reproduced from the tape and the additional sound information being produced through the sequencer module.
On the other hand, the MIDI clock signals to provide the time base for the additional sound information to be synthesized through the sequencer module of a known synchronized sound recording and reproducing system of the described nature are generated on the basis of those time intervals between the successive beat signals which are read from the internal memory of the system and the clock pulses which are constantly produced at a rate inherent in the system. These time intervals memorized in the internal memory of the system are respectively identical with those between the successive beat signals which have been read from the tape being played back. If it happens that the tape is subjected to an excessive force and is as a consequence partially elongated during playback operation, the time intervals represented by the beat signals read from the elongated tape are no longer identical with those represented by the beat signals which have been read from the original tape. Also prolonged as a result of the elongation of the tape are the sound signals recorded on the elongated tape, the rate of prolongation of the sound signals being equal to the rate of prolongation of the time intervals between the beat signals on the elongated tape. The sound signals on the tape elongated should therefore be reproduced using a time base generated in accordance with the beat signals read from the elongated tape. The fact is however that the time base for use in the reproduction of the sound signals from the elongated tape is generated on the basis of the beat signals read from the tape which was not elongated, rather than from the beat signals read from the elongated tape. The MIDI clock pulses to provide the time base for the additional sound information to be synthesized through the sequencer module are generated depending on the time intervals between the successive beat signals as well as the system clock pulses. Thus, a mismatch in time is invited between the sound information being read from the tape and the additional sound information being produced by the sequencer module.
The user of a synchronized sound recording and reproducing system may wish to start the playback of a tape in a partially wound condition, such a mode of operation being herein referred to as intervening-playback mode of operation. In this intervening-playback mode of operation, the time intervals between the beat signals being successively reproduced from the recording tape could not be correlated with the time intervals between the beat signals being successively read from the internal memory of the system. In other words, the sum of the values corresponding to the time intervals read out in succession from the internal memory of the system could not represent the actual physical locations on the tape which is being played back. This means that the synchronized operation between the tape recorder and the sequencer module practically can not be performed in the intervening-playback mode.
There may also be a case where the user of the system wishes to playback a recorded piece of sound information at a tempo expressed by himself. For this purpose, the user, or operator, of the system taps on the tapping switch while listening to the sound information being reproduced by the tape recorder. The tempo thus expressed by the operator in the form of the beats produced at the tapping switch is recorded as the beat signals on the tape, while the time intervals between the beat signals being produced in succession are stored in the internal memory of the system. The operator may further wish to start the sequencer module a desired period of time before the tape recorder is to be started for playback operation. This mode of operation is herein referred to as preliminary solo mode of operation. Such a preliminary solo mode of operation is however inoperable in a prior-art synchronized sound recording and reproducing system of the described nature. This is because of the fact that the beat signals are not reproduced from the tape until the tape recorder is started. In spite, furthermore, of the fact that the sequencer module is enabled to operate only in the presence of MIDI clock pulses which are produced on the basis of the time intervals between the successive beat signals from the tape recorder.
It is accordingly a first prime object of the present invention to provide an improved synchronized sound recording and reproducing system which is substantially free from an occurrence of a mismatch which would otherwise be invited between the sound information reproduced from the tape recorder and the additional sound information synthesized through the sequencer module if the accumulative values of the time intervals provided by the internal memory of the system were not representative of actual physical locations of the recording tape being played back.
It is another object of the present invention to provide an improved synchronized sound recording and reproducing system in which synchronism between the sound information from the tape recorder and the additional sound information from the sequencer module is maintained throughout operation of the system although the time-axis correlation between the time intervals read from the recording tape and those successively read from an internal memory incorporated in the system might be temporarily or momentarily lost or disturbed due to, for example, a dropout of a beat signal in the memory.
It is still another object of the present invention to provide an improved synchronized sound recording and reproducing system in which the beat signals recorded on the recording tape are detected from the tape in terms of the physical locations on the tape rather than in terms of the sequence in which the successive beat signals occur along the recording tape.
Yet, it is a second prime object of the present invention to provide an improved synchronized sound recording and reproducing system which is substantially free from an occurrence of a mismatch which would otherwise be invited between the sound information reproduced from the tape recorder and the additional sound information synthesized through the sequencer module if the recording tape happens to be partially elongated during playback of the tape.
It is still another object of the present invention to provide an improved synchronized sound recording and reproducing system in which sound signals are reproduced from the recording tape using a time base generator on the basis of time codes indicative of physical locations on the tape which is being played back, rather than the beat interval codes stored into the internal memory of the system before the playback operation with the particular tape was started.
Yet, it is a third prime object of the present invention to provide an improved synchronized sound recording and reproducing system which will permit the user of the system to start the playback of a recording tape in a partially wound condition, viz., in an intervening-playback mode of operation as herein so referred to.
It is still another object of the present invention to provide an improved synchronized sound recording and reproducing system in which reproduction of sound information by the tape recorder is started in synchronism with the sequencer module on the basis of the time codes indicative of physical locations on the tape which is in a partially wound condition, rather than the beat interval codes read from the internal memory of the system.
Yet, it is a fourth prime object of the present invention to provide an improved synchronized sound recording and reproducing system which is operable in a preliminary solo mode of operation as herein so referred to, starting the sequencer module a desired period of time before the tape recorder is to be started for playback operation.
It is still another object of the present invention to provide an improved synchronized sound recording and reproducing system in which reproduction of sound information through the sequencer module can be started prior to the start of the tape recorder on the basis of the time codes representing the first beat interval between the beat signals to be thereafter reproduced.